AlGaN/GaN heterostructure field-effect transistors (HFETs) have attracted much interest for high power and high frequency applications in recent years, because of their potentials for fast-switching with low-loss, high breakdown voltage (BV), high operating temperature, and good radiation hardness, among other reasons.
In power conditioning applications, switching at high frequency improves efficiency, and thus the device can also be used as an RF power amplifier in pulsed operations. However, the performance and reliability of AlGaN/GaN HFETs suffer from problems such as current slump and high gate and drain leakage currents, and these problems have to be solved in order to achieve practical applications.
Current slump may cause degradation of switching capabilities and increase in on-resistance. Passivation has been widely studied as a solution for suppressing current slump by encapsulating the surface states. However, while traditional passivation layers, such as Si3N4, can alleviate the current slump phenomena (see Ref. 1 below), they are not easily reproducible and tend to deteriorate the breakdown characteristics (see Refs. 2-3 below).
Other approaches, such as pre-passivation plasma treatments, annealing, and/or field-plates employments, can alleviate the current slump, as well (see Refs. 4-6 below), however, they tend to increase the on-resistance and/or create other problems.
For Schottky gates, the high leakage current precludes the realization of high breakdown voltage and incurs high power consumption, as well. There are many reports lately on the applications of insulators as gate dielectric and/or device passivation (see Refs. 7-9 below). While some can suppress the gate leakage current, they tend to induce current slump, lower the BV, or increase the on-resistance.
A solution for high-power fast switching devices, which can solve the entangled problems of current slump, persistent gate leakage, and premature breakdown, while maintaining a low on-resistance, is desirable.
There are a lot of references or prior art dealing with optimization of the material or devices related to power switches. For example, References 1-13, mentioned below: (These are also referred to throughout the current specification.)
1. B. M. Green, K. K. Chu, E. M. Chumbes, 1. A. Smart, 1. R. Shealy, L. F. Eastman, IEEE Electron Dev. Lett. 21, 268 (2000).
2. Y. Ando, Y. Okamoto, H. Miyamoto, N. Hayama, T. Nakayama, K. Kasahara, and M. Kuzuhara, IEDM Tech. Dig., 381 (2001).
3. H. Kim, R. M. Thompson, V. Tilak, T. R. Prunty, 1. R. Shealy, and L. F. Eastman, IEEE Electron Dev. Lett. 24, 421 (2003).
4. A. P. Edwards, 1. A. Mittereder, S. C. Binari, D. S. Katzer, D. F. Storm, and 1. A. Roussos, IEEE Electron Dev. Lett. 26, 225 (2005).
5. H. Kim, 1. Lee, D. Liu, and W. Lu, Appl. Phys. Lett. 86, 143505 (2005).
6. A. Brannick, N. A. Zakhleniuk, B. K. Ridley, 1. R. Shealy, W. 1. Schaff, and L. F. Eastman, IEEE Electron Dev. Lett. 30, 436 (2009).
7. C. Liu, E. F. Chor, and L. S. Tan, Semicond. Sci. Technol. 22, 522 (2007).
8. S. Yagi, M. Shimizu, M. Inada, Y. Yamamoto, G. Piao, H. Okumura, Y. Yano, N. Akutsu, H. Ohashi, Solid State Electron. 50, 1057 (2006).
9. A. Koudymov, N. Pala, V. Tokranov, S. Oktyabrsky, M. Gaevski, R. Jain, 1. Yang, X. Hu, M. Shur, R. Gaska, and G. Simin, IEEE Electron Dev. Lett. 30, 478 (2009).
10. M. A. Khan, G. Simin, 1. Yang, 1. Zhang, A. Koudymov, M. S. Shur, R. Gaska, X. Hu, and A. Tarakji, IEEE Trans. Microw. Theory Tech. 51, 624 (2003).
11. G. Simin, X. Hu, A. Tarakji, 1. Zhang, A. Koudymov, S. Saygi, 1. Yang, M. A. Khan, M. S. Shur, and R. Gaska, Jpn. 1. Appl. Phys. 40, L1142 (2001).
12. X. Hu, A. Koudymov, G. Simin, 1. Yang, M. A. Khan, A. Tarakji, M. S. Shur, and R. Gaska, Appl. Phys. Lett. 79,2832 (2001).
13. Y. C. Choi, 1. Shi, M. Pophristic, M. G. Spencer, and L. F. Eastman, 1. Vac. Sci. Technol. B 25, 1836 (2007).
However, here, we have introduced a new device, and a method for producing such a device, to optimize the performance further, with new features, as described in details below.
The inventors have based this invention partially based on the following paper: Titled “High Performance AlGaN/GaN Power Switch with HfO2 Insulation”, authored by Junxia Shi and Lester F. Eastman (of School of Electrical and Computer Engineering, Cornell University, Ithaca, N.Y. 14853), plus Xiaobin Xin and Milan Pophristic (of Velox Semiconductor Corp., Somerset, N.J. 08873).
However, please note that all the inventions and inventive steps are done at Cornell University, by the 2 Cornell researchers, i.e. the current (and only) 2 inventors on the inventors list, for the current application.